Inertia operated shock load switch



May 22, 1956 E. THOMSON INERTIA OPERATED SHOCK LOAD SWITCH 2Sheets-Sheet 1 Filed Dec. 22. 1952 y 1956 E. THOMSON INERTIA OPERATEDSHOCK LQAD SWITCH 2 Sheets-Sheet 2 Filed Dec. 212, 1952 United StatesPatent INERTIA OPERATED SHOCK LOAD SWITCH Edward Thomson, Mount Vernon,Iii. Application December 22, 1952, Serial No. 327,254

13 Claims. (Cl. 200--61.46)

This invention relates to switches and is more particularly directed toan inertia actuated switch responsive to shock loads and whichincorporates a magnetic element that assists in the operation of theswitch.

One of the objects of the invention is to provide an inertia operatedswitch for a power circuit in which a magnetic over center actuator isemployed.

Another object of the invention is to reduce the number of operatingparts in a shock load release switch.

Another object of the invention is to provide an inertia actuated shockload release switch wherein a magnetic element is employed that assistsin completing the relative motion of inertia element and the body of theswitch after the relative movement of inertia element and body passesthe mid or center point of its movement.

Another object of the invention is to provide a shock load releasemechanism that can be placed in the drive motor circuit for opening thelatter after the driven machine accelerates or decelerates greater thana prcdetermined rate.

A further object of the invention is to provide an inertia operatedswitch that can be quickly and sensitively adjusted for varying shockload conditions.

The invention consists in the provision of a shock load release switchwherein a make and break switch is actuated in response to the relativemovement of an inertia device and the rotatable element with which it isasso ciated after said relative movement changes exceed a predeterminedrate and wherein a magnetic element aids in completing said relativemovement initiated by the inertia device.

in the drawings:

Fig. 1 is an end view of a device incorporating the invention,

Fig. 2 is an enlarged view taken substantially along the line 2-2 ofFig. i,

Fig. 3 is a view taken substantially along the line 3-3 of Fig. 2,

Fig. 4 is a view similar to Fig. 3 but showing the parts in differentoperative positions,

Fig. 5 is a sectional view similar to Fig. 2 of a modifled form of theinvention,

Fig. 6 is a sectional view taken along the line 6-6 of Fig. 5 showingthe switch in operative or closed position,

Fig. 7 is a view similar to Fig. 6 showing the switch in open position,and

Fig. 8 is an enlarged detailed structural view showing the method ofassembly of the parts.

The invention is embodied in the several views of the drawings in whichthe numeral 1 designates the casing for the shock load release switch.This is an annular body in which a shaft 2 is rotatably mounted in acylindrical bearing holder member 3 suitably secured to the casing i.The cylindrical member 3 is provided with suitable bushings 4 serving asbearings for the shaft. The shaft is normally equipped with a pulley orrigid coupling (not shown) and is placed between the load and r2,747,041 Patented May 22,1956

ice

the motor that drives the machine on which the. release switch isinstalled. The invention is particularly useful for the driving ofmachine tools such as drill presses, tapping machines or similardevices. The machine drive is interconnected with the shaft 2 so thatthe shock load release switch is driven in unison therewith. The shaft 2extends into the casing 1 and a cup-shaped inertia member 5, preferablybeing made of non-magnetic material, is supported on the shaft bysuitable bushings 6. The inertia member is adapted to rotate with orrelative to the shaft depending upon load conditions in the device.

The shaft 2 is provided with an armature 7 to which it is suitablysecured and disposed between the ends of an annular magnet 8. Thismagnet is preferably formed from a paramagnetic material and the endsare spaced apart to form a gap in which the armature 7 is received. Thepreferred material is that sold under the trade name of Alnico or anysuitable steel, and the use of an electromagnet is also contemplated inlieu of the permanent magnet shown. The magnet is suitably held withinthe cup-shaped inertia member and has an air gap between the endsthereof. During normal operation a bridging device 9 is secured to thearmature 7 and is intended to bridge the gap between the ends of themagnet 8 to thus permit a freer and better flow of the magnetic lines offorce. it is also used as a counterweight to produce more correctdynamic balance. I

The shaft 2 is provided with a cam 10 preferably made by milling off aportion of the shaft so as to form a flat surface thereon. The cam 10moves the movable element 11 of a switch 12 so as to make and break acontrol circuit for the driving motor previously discussed, the element11 being pivoted to the closure 24 for the inertia member 5. The movableelement has a contact 13 secured thereto engageable with a fixed contact13' suitably fastened to the base of the switch mounted on the closurefor the inertia member 5. As the shaft 2 and the armature 7 moverelative to the inertia member, the movable element of the switch willmove with respect to the fixed element thus separating the contacts 13and 13 or bringing together depending upon the direction of motion ofthe armature 7 relative to the inertia device. The relative movement ofarmature and inertia device is based upon the change in the rate of thespeed of the driven device or machine and when this rate exceeds apredetermined amount the inertia device will continue rotating in itsnormal speed and cause the switch contacts to separate thus interruptingthe circuit to the drive motor, the separation or engagement beingcaused by the action of cam 1i) and follower 11.

The engagement of the armature 7 with one end of the magnet 8 causes theinertia element to be rotated with the shaft 2 and the armature 7 andthe relative motion discussed above takes place upon the predeterminedchange in rate of rotation of the driven device. The amount of shockload at which the armature 7 is separated from the adjoining end of themagnet, as for instance shown in Fig. 3, will depend upon the air gapthat is present between the armature and the end of the magnet. This gapis regulated by means of screws 14 and 1 also designated as stationarypoints threaded into the inertia device. These screws preferably arenonmagnetic so that they will not influence the adherence of thearmature to the magnet. Thus by altering the size of the gap between thearmature and the end of the magnet the amount of shock load required toproduce an opening or a closing of the switch contacts 13 and 13 will bereadily determined. Enough clearance is left between cam surface 10 andthe cam follower 11 to allow for the adjustment of armature 7 relativeto the adjacent end of the magnet 8 to form an air gap when the contacts13 and 13' are in closed position.

3 The casing is provided with a pair of conductors 15 and 16' suitablyheld in the removable cover 17' of the casing 1. Suitable insulatingbushings and brush holders 18 are provided to receive. these conductorsin the cover and each has a tubular extension 19 thereon that slidablyholds brushes 2%). Springs 21 are provided between the brushes and thebase of the tubular extensions to force the brushes into contact withcollector rings 22 and '23 suitably secured to and insulated from theremovable closure 24 for the cup-shaped inertia member 5. Contacts 13and 13 are electrically connected to collector rings 22 and 23respectively and as previously indicated are in the circuit of thedriving motor. A manual switch 25 (Fig. 2) is connected across theconductors 15 and 16 for initially starting the drive motor in the eventthe contacts 13 and 13' may not be in engagement with each other. Themember 3 is provided with a grease fitting 26 for lubricating shaft 2.

During the operation of the device should the machine tool or othermechanism to which the shock load release switch is connected encounterin its operation a shock load that would tend to break a drill bit, tap,other tool, or cause machine breakage and which would not open thecircuit breaker or blow fuses because of the extremely short period oftime in which the obstruction to the operation of the machine occurs theinstant device will open the drive motor circuit. Assuming that it is adrill bit that is jammed, the shaft 2 being driven by the drill bitspindle which, in turn, is driven by the motor that is connected to theconductors 15 and 16, the switch contacts 13 and 13 will be caused toopen due to relative movement between the cam and the contacts by reasonof the momentum of the inertia member causing the armature 7 to shiftfrom the Fig. 4 to the Fig. 3 position. In other words when a momentaryslow-down of shaft 2 occurs the armature 7 (Fig. 4) will also slow downwhile the inertia membercarrying the switch will continue rotating untilthe condition of Fig. 3 is attained. When the shift takes place thecontacts 13 and 13' will be separated thus breaking the circuit to thedrive motor.

When the device is to be started the switch 25 connected across theconductors and 16 will be closed thus permitting the motor to be startedand since the mass of the inertia member is far greater than that of theshaft 2 and the armature 7 the latter will rotate relative to theinertia member so as to restore it to the Fig. 4 position. At this timethe switch may be reopened and since the armature 7 now is in contactwith one end of the magnet 8 or the adjusting screw 14' it will causethe inertia member to rotate with the armature. Motion will continueuntil the machine being driven encounters another sudden shock loadwhereupon the performance of the device will be repeated. It is thusapparent that a suitable and reliable device has been provided whichbreaks a circuit to a drive motor when a sudden load is applied to themachine which is of such a nature that will not open the circuit breakeror blow a fuse that may be connected in the power line leading to themotor. This device reduces tool breakage and damaged goods to such anextent that breakage is practically unknown and prevents burn-outs ofthe driving motor and permits restoration of the operation of themachine when the cause for the shock load has been removed. It isassumed that the direction of rotation of the inertia member and theshaft 2 is normally in the direction of the arrows shown in the figuresof the drawing.

A modified form of the invention is shown in Figs. 5-S in which thenumeral 30 designates a stationary casing in which a shaft 31 is rotablymounted. An inertia ring 32 is secured to discs 33 and 34 rotatablysupported on the shaft 31 by means of suitable bushings.

A nonmagnetic spacer is secured to the shaft 31 that has a lengthsubstantially equal to the width of the inertia ring 32. Secured to thespacer 35 is a magnet 36 made of paramagnetic material and is preferablymade from each other.

4 a material sold under the brand name of Alnico. The armatures 37' and37" for this magnet are extensions of the inertia ring 32, whose endsare turned radially inward to form the armatures. Screws 38 and 39 arethreaded into the armatures for controlling the size of the air gap andthe amount of shock load required to cause the inertia ring and magnetto rotate relative to The screws are preferably formed from a suitablenonmagnetic material in order not to influence the action of armatureand magnet.

A switch .8, constructed in the same way as switch 11, is securedto thedisc 34. A cam 41 cut in shaft 31 cooperates with a follower 42 foropening and closing the points on the switch 4.0. Collector rings 43 and44 are secured to and insulated from the disc 34 and serve the samepurpose as the collector rings in the disciosure of Figs. 1-4.

The operation of this device is the same as that defined above. It isassumed that the brush structure and starting switch are provided asabove.

In each of the above disclosures the switches 11 and 49 are equippedwith springs 45 for normally holding points 13 and 13 in engagement witheach other. While screws 38, 39 and 14, 14 have been defined asnonmagnetic it is not a strict necessity that they be limited thereto.Each screw adjusts the air gap but performs different functions. Gnescrew determines the reduction in speed necessary to cause relativemotion of armature and magnet while the other regulates the resetting ofthe armature for starting purposes when switch 25 is closed.

What I claim is:

l. A shock load release switch comprising a casing, a shaft rotatablymounted therein, an annular inertia device mounted on said shaft forrotation with or relative to said shaft, an annular magnet secured insaid inertia device and having a gap therein, an armature secured tosaid shaft and located within said gap and in contact with one end ofsaid magnet, a non-magnetic adjusting means located in each end of themagnet for adjusting the spacing between the armature and magnet, aswitch mounted on said inertia device, and a cam in said shaft foractuating said switch upon relative rotational movement of said inertiadevice and shaft, said armature aiding in completing the relativemovement as it moves through said gap into engagement with the other endof said magnet.

2. A shock load release switch comprising a casing, a shaft rotatablymounted therein, an annular inertia device mounted on said shaft forrotation with or relative to said shaft, an annular magnet secured insaid inertia device and having a gap therein, an armature secured tosaid shaft and located within said gap and in contact with one end ofsaid magnet, a member mounted on said armature for substantiallybridging the gap in said magnet, a switch mounted on said inertiadevice, and a cam in said shaft for actuating said switch upon relativerotational movement of said inertia device and shaft, said armatureaiding in completing the relative movement as it moves through said gapinto engagement with the other end of said magnet.

3. A shock load release switch comprising a casing, a shaft rotatablymounted therein, an annular inertia device mounted on said shaft forrotation with and relative to said shaft, an annular magnet secured insaid inertia device and having a gap therein, an armature secured tosaid shaft and located within said gap and in contact with one end ofsaid magnet, a non-magnetic adjusting means located in each end of themagnet for adjusting the spacing between the armature and magnet, amember mounted on said armature for substantially bridging the gap insaid magnet, a switch mounted on said inertia device, and a cam in saidshaft for actuatingv said switch upon relative rotational movement ofsaid inertia device and shaft, said member aiding in completing therelative rotational movement as it moves through said gap intoengagement with the other end of said magnet.

4. A shock load release switch comprising a casing, a shaft rotatablymounted in said casing, an inertia element, means for supporting saidinertia element upon said shaft for rotation with and relative to saidshaft, a make and break switch mounted on said means, a cam on saidshaft, means connecting said cam and switch to actuate same uponrelative rotation of said shaft and inertia element; and a magnetcarried by said shaft to assist in completing the relative movement, theinertia element forming an armature for said magnet.

5. A shock load release switch comprising a casing, a shaft rotatablymounted in said casing, an inertia element whose ends are projectedradially inward to form a gap between the ends, means carried by saidshaft for supporting said inertia element about said shaft for rotationtherewith or relative thereto, a magnet mounted on said shaft, theinturned ends of said inertia element forming armatures for said magnet,a make and break switch mounted on said means; and a cam on said shaftfor actuating said switch upon relative rotation of said inertia elementand shaft, whereupon said magnet moves from a position adjacent onearmature to a position adjacent the other.

6. A shock load release switch comprising a casing, a shaft rotatablymounted in said casing, an inertia element formed into a circle aboutsaid shaft and whose ends are directed radially inward to form armaturesfor a magnet, means carried by said shaft for supporting said inertiaelement, a make and break switch mounted on said means, cam means onsaid shaft for operating said make and break switch, a magnet mounted onsaid shaft adapted to swing between said armatures, upon relativerotation of said shaft and inertia element; and means for adjusting theair gap between said magnet and each armature.

7. A shock load release switch comprising a casing, a shaft rotatablymounted in said casing, an inertia element formed into a circle aboutsaid shaft and whose ends are directed radially inward to form armaturesfor a magnet, means for supporting said inertia element, a make andbreak switch mounted on said means, cam means on said shaft foroperating said make and break switch, a magnet mounted on said shaftadapted to swing between said armatures, upon relative rotation of saidshaft and inertia element; a screw extending through one of saidarmatures for engagement with said magnet for determining when saidshaft and inertia device will rotate relative to each other to open saidmake and break switch; and a screw means in the other armature fordetermining when reverse relative rotation will occur for closing saidmake and break switch.

8. In an inertia actuated shock load responsive device, a casing for thedevice, a rotary shaft bearinged in said casing, a member fixed to saidshaft so as to be movable with said rotary shaft and disposed withinsaid casing, a second member disposed within said casing so as to bemovable relative to said rotary shaft, said second member providing agap to receive said fixed member and limit the extent of relativemovement between such members, one of said last mentioned relativelymovable members being formed from magnetic material and the otherthereof acting as an armature for the magnetic member, said relativelymovable members being magnetically coupled when in adjacence at onelimit of the gap to rotate together with said shaft and said secondmember being freed from said magnetic coupling to rotate relative tosaid fixed member to the other limit of the gap upon a shock loadreaction in said shaft, and circuit controlling switch means in saidcasing adapted to have a circuit make position in said first mentionedmagnetically coupled position of said members and a circuit breakposition in said second mentioned relatively rotated position of saidmembers, said switch being operated by said members.

9. in an inertia actuated shock load responsive device, a casing, arotary shaft bearinged in said casing, 21 first member in said casingcarried by said shaft to respond to shaft rotation, a second member insaid casing bearinged upon said shaft to rotate relative to said shaftand providing a gap to receive said first member and allow limitedrelative movement between such members, one of said members being amagnet and the other an armature for the magnet member whereby suchmembers have a magnetic coupling effect to retain them, adjacent onelimit of relative movement allowed by the gap in said second member,adjustable means carried by said second member adjacent the gap toengage said first member and adjust the air gap spacing of said membersfor varying the strength of the magnetic coupling effect at said onelimit of relative movement, said magnetic coupling effect at said onelimit position being broken upon a shock load reaction in said shaft,and circuit controlling switch means between said relatively movablemembers normally in circuit make position with said members magneticallycoupled together at said one limit and in circuit break positionfollowing a shock load reaction in said shaft breaking the magneticcoupling effect between said members, said switch being operated by andin response to relative movement of said members.

10. In an inertia actuated shock load responsive device, a casing, arotary shaft bearinged in said casing, a first member carried by saidshaft within said casing, a second member relatively movably carried bysaid shaft adjacent said first member, said second member having a gaptherein to receive said first member and limit relative movement betweensaid members, one of said members being magnetic and the other acting asan armature whereby said members are magnetically coupled at each limitof relative movement in the gap, adjustable means on one of said membersin position to be engaged by the other member at the limit positions inthe gap for determining the strength of the magnetic coupling efiect byadjusting the air gap space between said members, circuit controllingswitch means carried by said second member adjacent said shaft, and cammeans on said shaft to actuate said switch means toward circuit breakposition upon a shock load reaction in said shaft causing relativemovement of said members to one limit of the gap, the opposite relativemovement of said members causing cam actuation of said switch means tocircuit make position.

11. The inertia actuated shock load responsive device set forth in claim10, wherein said adjustable means is nonmagnetic.

12. The inertia actuated shock load responsive device set forth in claim10, wherein said second member is formed of magnetic material and actsas the magnetic member.

13. The inertia actuated shock load responsive device set forth in claim10, wherein said first member is formed of magnetic material and acts asthe magnetic member.

References Cited in the file of this patent UNITED STATES PATENTS1,638,718 Vroman Aug. 9, 1927 2,280,114 Athy Apr. 21, 1942 2,294,605Newell Sept. 1, 1942 2,294,606 Newell Sept. 1, 1942 2,415,344 EksergianFeb. 4, 1947

